System and Method for Network Handover

ABSTRACT

The invention provides for a telecommunications system and related method of handover from a first radio access technology to a second radio access technology for a mobile radio communications device within a mobile radio communications network, and including determining a timing advance value associated with the second radio access technology, and the method employing positional data of the device within the network for determining the said timing advanced value.

TECHNICAL FIELD

The present invention relates to a system and method for networkhandover to be adopted, in particular, in relation to a mobile radiocommunications device required to handover from the first radio accesstechnology to a second radio access technology.

BACKGROUND ART

In order to realise the full advantages available with multimode radiocommunication devices, such as multimode cellular telephones, it isrecognised that such devices may be requested to change from operationwith the radio access technology of one network, to operation with adifferent radio access technology of a second network. For example, withthe increasing availability and use of third generation networks, it islikely that such networks will be overlaid with earliersecond-generation networks. Users of such networks will be dividedbetween both depending on, in particular, user priority, the servicerequested, the coverage and other operator strategies so as toeffectively manage network resources.

During a call, a user's terminal may therefore be requested to hand overfrom, for example, a Universal Mobile Telephone Services (UMTS) networkcell to a Global Systems for Mobile communications (GSM) network cell.In order to limit the impact on the terminal and that might bediscernable to the user of that terminal, any such handover shouldhappen as quickly and smoothly as possible and with minimum interruptionto the call currently in place. A variety of data is required in orderto achieve handover with minimum disruption and one particularlyimportant piece of information required concerning the cell to which theterminal is to be handed over to comprises the timing advanceinformation.

Such information is required so that appropriate synchronisation to thenew cell can be achieved so that the communication signal sent to thatcell can be sent at an appropriate time so as to reach the targetBasestation System (BSS) at the appropriate time slot.

As currently known, if, for example, the terminal has measured theobserved time difference to the GSM cell while operating on the UMTScell, and the network has also signalled the real time differencebetween for example a Node B and the BSS to the terminal, the terminalcan then calculate the new timing advance value. However, if sucharrangement does not prove possible, the BSS then has to calculate thetime and advance value by requesting the terminal to transmit accessbursts.

Such arrangements are however disadvantageously limited due to theadditional signalling created and the delays in handover that can arise.

DISCLOSURE OF INVENTION

The present invention seeks to provide for a network handover system andmethod having advantages over known such methods and systems.

According to one aspect of the present invention, there is provided amethod of handover from a first radio access technology to a secondradio access technology for a mobile radio communications device withina mobile radio communications network, and including determining atiming advance value associated with the second radio access technology,the method employing positional data of the device within the networkfor determining the said timing advance value.

Through the use of the positional data, which can be obtained inaccordance with any appropriate position measuring arrangement, such asGPS-based or otherwise, the timing advance value can be calculatedwithout requirement for the excess signalling that arises at the time ofhandover in accordance with known arrangements. A far faster processthan is currently available can therefore be provided.

The advantageous shorter interruptions that arise due to the fasterhandover and reduction in signalling advantageously leads to improvedresource utilisation and a reduction in the perceived inconvenience andinterruption for the user.

The present invention can advantageously make the timing advanceinformation available within the handover command which assists inovercoming the need for access burst transmissions and subsequentsignalling of the timing advance information.

Preferably, the location of the BSS associated with the second radioaccess technology is also determined and employed in calculating thetiming advance value.

Advantageously, the aforementioned positional data is determined priorto generation of the handover command.

The timing advance value is advantageously determined within the networkand transmitted to the terminal as required.

In particular, the Serving Radio Network Controller (SRNC) is arrangedto receive the positional information which is then advantageouslypassed via the Core Network (CN) to the BSS. The timing advance valuecan advantageously be signalled to the device within the handovercommand.

Of course, as an alternative, the timing advance can be calculatedwithin the device.

According to another aspect of the present invention, there is provideda mobile communications system arranged for operation with a first radioaccess technology and a second radio access technology and includingmeans for initiating the handover of a mobile radio communicationsdevice from the first radio access technology to the second radio accesstechnology, wherein the means for initiating the handover includingmeans for determining a timing advance value associated with the secondradio access technology and wherein such means is arranged to employpositional data of the terminal within the network for determining thesaid timing advance value.

The system can be arranged to operate in accordance with theadvantageous further features as discussed above.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a diagrammatic representation of a currently specifiedhandover procedure from a UMTS to the GSM cell,

FIG. 2 is a representation of the handover procedure according to anembodiment of the present invention,

FIG. 3 is a schematic flow diagram illustrating an embodiment of thepresent invention, and

FIG. 4 is block-timing diagram illustrating advantages arising inaccordance with the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

As will therefore be appreciated, the present concept provides for theadvantageous use of positional information of the terminal so as toprovide timing advance information to the terminal in a manner whichleads to a faster handover procedure exhibiting a reduced signallingoverhead.

In order to illustrate the present invention further, there now followsa discussion of the currently known handover procedure from a UMTS cellto a GSM cell and as specified in the current 3rd Generation PartnershipProject (3GPP).

Upon the SRNC deciding that handover from the UMTS cell to a GSM cell isrequired, it sends a RELOCATION REQUIRED message to the CN which servesto initiate the procedure for handover to the GSM cell. During thehandover process, the link to the Universal Mobile Telephone ServicesTerrestrial Radio Access Network (UTRAN) is dropped and a new link isset-up to the BSS associated with the GSM cell.

A HANDOVER FROM UTRAN command is then sent to the terminal and includesinformation such as the frequency, channel description, transmit powerlevel and timeslot etc that assists the terminal in setting up the newlink to the BSS associated with the GSM cell, It should be noted that aHANDOVER ACCESS message can be optionally requested by the network. Theaforementioned arrangement allows the BSS to calculate the timingadvance value which can then be signalled by the BSS to the terminal aspart of the PHYSICAL INFORMATION message.

As will be appreciated, the timing advance value is a key physical layerparameter which enables the terminal to commence its normal bursttransmission at the appropriate time so as to reach the BSS associatedwith the GSM cell within the specified timeslot.

The known specification also suggests that the timing advance value canbe calculated by the terminal itself if it can be arranged to measurethe observed time difference to the GSM cell while connected to the UMTScell and if the network has signalled the real time difference betweenthe Node B and the RSS.

If the terminal is not able to measure the aforesaid observed timedifference, or the network is not in a position to signal the real timedifference between the Node B and the BSS, then the timing advancecannot be calculated at the terminal but rather has to be signalled tothe terminal by the network as discussed above.

With the arrangement discussed above, the handover access burst allowsthe network to estimate the timing advance and deliver an appropriatevalue for the timing advance to the terminal. It should be noted thatthe access burst may have to be transmitted several times before thenetwork returns the timing advance information.

However, in accordance with the present invention, it is identifiedthat, if the network can estimate the timing advance prior to thehandover command, then the additional signalling mentioned above, andthe associated delay, can advantageously be avoided.

According to the present invention, it is proposed that the networkemploy determination of the terminal position so as to derive the timingadvance value.

The use of positional data is considered advantageous since the typicalpositioning accuracy required for location services with mobileterminals effectively operates within sub-100m accuracy. This level ofaccuracy exceeds the required timing advance accuracy. On this basis, noadditional powerful processing is required to calculate the timingadvance from the position estimation since an appropriate level ofaccuracy is already inherent in the data provided.

As a further advantage, within UMTS there is an optional provision tosupport position reporting by the terminal. Also, in view of commercialconsiderations relating to the provision of location based value-addedservices and regulatory requirements for emergency services, the abilityfor location determination and position reporting is increasinglyavailable and can readily be supported by a dual-mode terminal. Thepresent invention can therefore readily be incorporated to currentlyavailable systems.

Thus, there is little, if any, overhead in requiring the network toobtain terminal position data, or to request such data prior tohandover. Knowledge of the terminal position and the location of theNode B, and the new BSS associated with the radio access technology towhich the terminal is to handover is then advantageously employed tocalculate the timing advance value which can itself then be signalled tothe terminal as part of the HANDOVER FROM UTRAN command.

An example of an appropriate procedure embodying the present inventionis illustrated by way of FIG. 2 and which relates to a handover fromUTRAN to GSM by means of positional information.

As will be appreciated from FIG. 2, the SRNC obtains the positioninformation prior to requesting handover to the GSM cell. Thisinformation is then passed via the CN to the new BSS and this new BSS isthen arranged to signal the timing advance value to the terminal via theHANDOVER FROM UTRAN command.

The information flow between the various entities discussed above isillustrated further with reference to FIG. 3.

The system illustrated in FIG. 3 comprises a dual mode terminal 10, NodeB 12 associated with a radio network controller 14 and a representationof the core network 16.

Also illustrated are a base station controller 18 and base transceiver20 forming, in combination, the new base station system.

The procedure commences at the terminal 10 with the delivery, by way ofarrows 22, 24 and 26 of positional information relating to the terminal10, Node B 12 and radio network controller 14 respectively, to the corenetwork 16.

On the basis of this positional information, the timing advance signalis calculated at the core network 16 and then returned by way of arrows28 to the terminal 10 by way of the radio network controller 14 and NodeB 12.

The receipt of the handover command signal, including the timing advancevalue, at the terminal 10 allows for the generation of a signal 30 fromthe terminal 10 confirming that the handover is complete and also withinthe appropriate timeslot to the new base station system associated withthe GSM network.

Turning now to FIG. 4, there is provided an illustrated although not toscale, of the potential time savings achievable in accordance with thepresent invention.

The upper half of the diagram illustrates the handover procedure fromUMTS to GSM in accordance with current standard procedure and whichillustrates UMTS control signalling 32, and GSM control signalling 34,as required so as to complete the handover procedure and commencetransmission of the GSM traffic 36.

By comparison, the lower part of the diagram illustrates the handoverfrom UMTS to GSM in accordance with an embodiment of the presentinvention and which illustrates how the completed handover andtransmission of GSM traffic 38 can be achieved without requiring thesame level of GSM control signalling as arising in the prior-art.

As will be appreciated, the present invention exhibits a variety ofadvantages. In particular, through use of the invention, the use ofmultiple excess bursts, and the physical information message, can beavoided so as to lead to an advantageous reduction in the signalrequired for handover.

The faster handover from UTRAN to GSM can therefore be achieved so as tolead to less inconvenience and potential disruption for the user.

Current 3GPP specifications provide for the capability to support thepresent invention without significant changes in view of theimplementation of position determination inherent in such specification.

Further, the invention advantageously employs information that iscurrently available within the network so as to provide the informationrequired by the terminal to achieve the accurate and speedy handover.

Also, relatively simple processing can be employed to process theposition information in order to provide the timing advance early to theterminal.

As noted previously, the invention can also be readily arranged so thatthe timing advance is calculated within the handset, rather than withinthe network and with appropriate employment of a Radio Resource LCSProtocol (RRLP) signalling information.

Finally, below is the listing of parts of abbreviations and theirmeanings appearing in FIGS. 1 and 2:

AS: Access Stratum BSC: Base Station Controller CN: Core Network CRNC:Controlling RNC

DRNC: target or Drift RNC

DSCH: Downlink Shared Channel GSM: Global System for MobileCommunications

Iu: Interface between Radio Network Controller and Core Network(s)Iub: Interface between Radio Network Controller and Base Stations (BSs)

MAC: Medium Access Control MS: Mobile Station RAN: Radio Access NetworkRANAP: Radio Access Network Application Part RLC: Radio Link ControlRNC: Radio Network Controller RRC: Radio Resource Control SRNC: Servingor Source Radio Network Controller UE: User Equipment UTRAN: UniversalMobile Telecommunications (UMTS) Terrestrial Radio Access Network

Uu: Interface between User Equipment and Base Station

1. A method of handover from a first radio access technology to a secondradio access technology for a mobile radio communications device withina mobile radio communications network, and including determining atiming advance value associated with the second radio access technology,the method characterized by employing positional data of the devicewithin the network for determining the said timing advance value.
 2. Amethod as claimed in claim 1, wherein the timing advance value is alsodetermined on the basis of the location of the base station systemassociated with the second radio access technology.
 3. A method asclaimed in claim 1, wherein the positional data of the device isdetermined prior to handover.
 4. A method as claimed in claim 1, whereinthe timing advance value is determined within the network.
 5. A methodas claimed in claim 4, wherein the positional data is provided within aserving radio network controller of the network.
 6. A method as claimedin claim 5, wherein the positional data is delivered by way of a corenetwork arrangement to the basestation system.
 7. A method as claimed inclaim 5, wherein the timing advance value is signalled to the devicefrom the basestation system.
 8. A method as claimed in claim 7, whereinthe timing advance value is included within the handover command asreceived by the device.
 9. A method as claimed in claim 1, wherein thetiming advance value is determined within the device.
 10. A mobilecommunications system arranged for operation with a first radio accesstechnology and a second radio access technology and including means forinitiating the handover of a mobile radio communications device from thefirst radio access technology to the second radio access technology,wherein the means for initiating the handover including means fordetermining a timing advance value associated with the second radioaccess technology and wherein such means is arranged to employpositional data of the device within the network for determining thesaid timing advance value.
 11. A system as claimed in claim 10, andarranged such that the timing advance value is also determined on thebasis of the location of the basestation system associated with thesecond radio access technology.
 12. A system as claimed in claim 10, andarranged such that the positional data of the device is determined priorhandover.
 13. A system as claimed in claim 10, and arranged such thatthe timing advance value is determined within the network
 14. A systemas claimed in claim 13, and arranged such that the positional data isprovided within a serving radio network controller.
 15. A system asclaimed in claim 14, and arranged such that the positional data isdelivered by way of a core network arrangement to the basestationsystem.
 16. A system as claimed in claim 13, and arranged for signallingthe timing advance value to the device from the basestation system. 17.A system as claimed in claim 16, wherein the timing advance value isincluded within the handover command as received by the device.
 18. Asystem as claimed in claim 10, and arranged such that the timing advancevalue is determined within the device.
 19. A method of handover from afirst radio access technology to a second radio access technology for amobile radio communications device within a mobile radio communicationsnetwork and substantially as hereinbefore described with reference to,and as illustrated in, FIGS. 2, 3 and 4 of the accompanying drawings.20. A mobile radio communications system arranged for a handover from afirst radio access technology to a second radio access technology andsubstantially as hereinbefore described with reference to FIGS. 2, 3 and4 of the accompanying drawings.